A processor has access to two levels of memory. It takes $5$ ns to access words from level $1$ and $100$ ns to access words from level $2.$ If a word to be accessed is in level $1,$ then the processor accesses it directly. If it is in level $2,$ then the word is first transferred to level $1$ and then accessed by the processor,

Suppose that $90\%$ of the memory accesses are found in level $1.$ What is the average time to access a word?